[R-390] Solid State R-390, Why Not?

Sun, 11 Aug 2002 18:06:49 -0400

Hi,

There is a closely related thread that comes up from time to time. More or
less it runs "what can you do to improve an R-390A". Needless to say it also
creates quite a bit of traffic when it comes up. To really get things going
you need to combine the two threads.

What's right about a '390 - the tuned front end, the IF filters, The nice
big knobs and dials, the dual audio outputs.

What's wrong with a '390 (compared to say an RF-590) - Frequency stability,
dynamic range, harder to tune from 5.8 to 6.2 MHz, not as easy to use on SSB

What's commonly done to a '390 - upgrade the AGC and audio

Assuming the objective is to "fix what's wrong" *without* getting in trouble
:

1) The gain distribution of the radio is based on stuff that has a lot less
gain than the solid state stuff you can get today. A simple conversion puts
way to much gain in front of the IF filters. I suspect that getting the
dynamic range up to modern standards will take more effort than it's worth.

2) The impedance levels of *everything* are way higher than what you would
use with solid state parts. This starts with the RF coils and runs right
through the audio transformers. This is true both in terms of the real part
of zin and zout as well as the capacitances. Getting all the RF and IF stuff
to track with a lot more C padding it all will be a pain. If you retain the
high impedance coils getting the feedback capacitance under control will be
a major undertaking.

3) To improve the frequency stability you need a different arrangement for
the crystal oscillator section and the PTO. Simply putting trimmers on the
crystals would make the radio a bit more user friendly. Mechanically this is
a messy process. If you replace the PTO and crystal deck with a synthesizer
the interface issues will be at least as messy.

The stuff that's easy to fix is all in the audio module. The stuff that has
all the trouble above may not be worth it. Audio modules are a dime a dozen
out there. Taking a junk audio module and fiddling it around is rarely an
item of discord on the list.

So here's what I'd do to an audio module:

1) take care of the ballast tube issue, *maybe* run a jumper or two to a
tube socket or two.

2) Put in a couple of real audio stages (two 600 ohm, one 8 ohm)

3) Put in a real regulator for the high voltage(s)

Assuming you start with a junk module you have taken care of about 80% of
what can be done and it's pretty much reversible if you swap back the
original module.

    Enjoy!

        Bob

----- Original Message -----
From: "Tom M." <[email protected]>
To: "blw" <[email protected]>; <[email protected]>
Sent: Saturday, August 10, 2002 8:26 AM
Subject: [R-390] Solid State R-390, Why Not?

> Gentlemen?
>
> Why not solid state a R-390A?
>
> If it was very rare I'd say no.  But as plentiful as they are, why not
advance
> the range of the 390A hobby?
>
> Regarding the grandpa with two Jags, I guess I don't need to go into the
joke
> as to why Jags are sold in pairs.
>
> 73 Tom
>
> Favorite bumper sticker: "THE PARTS WHICH ARE FALLING FROM THIS MACHINE
ARE OF
> THE FINEST BRITISH MANUFACTURE"
>
>
> --- blw <[email protected]> wrote:
> >
> > > Saddest part is that the Jags are a very reliable car if you maintain
them
> > > properly. Unfortunately too many people want the looks but have all
they
> > can
> > > do
> > > to change the oil regularly. At least their problems are solved now
with
> > the
> > > Forduars. Plug-n-play mentality, not unlike ricebox vs. tube rigs.
> > >
> > > 73, Todd/'Boomer'  KA1KAQ
> >
> >
> > My grandfather had a couple of new Jags about 10 years ago. I drove them
> > both and they were absolutely depressing. One had a lot of interior
parts
> > falling off and lying on the floor mats. Nice acceleration. I couldn't
hold
> > either in a straight line no matter how smoothly I drove it. They
wandered
> > all over the place. I grew up with a Jag that my dad had back around
> > 1957-58. It was beautiful. That is one of the reasons I was so depressed
> > with Jags 10 years ago.
> >
> >
> > Barry
> >
> > _______________________________________________
> > R-390 mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/r-390
>
>
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